Saturday. Send my sister off to Cameroon.
1212.4500
Systematic effects in large-scale angular power spectra of photometric quasars and implications for constraining primordial nongaussianity
Pullen, Hirata
Primordial non-Gaussianity of local type is predicted to lead to enhanced halo clustering on very large scales. Quasars at z>2 are promising tracers for constraining non-G using this effect. However, large-scale systematics can also mimic this signature of non-G. In order to assess the contribution of systematic effects, cross-correlate overdensity maps of photometric quasars from SDSS DR6 in different z ranges. Find that the maps are significantly correlated on large scales, even though the expectation is such that the angular distribution of quasars at different redshift to be uncorrelated. THis implies that the quasar maps are contaminated with systematic errors. Investigate the use of external templates that provide information on the spatial dependence of potential systematic errors to reduce the level of spurious clustering in the quasar data. Find that templates associated with stellar density, the stellar color locus, airmass, and seeing are major contaminants of quasar maps, with seeing having the largest effect. Using template projection, decrease the significance of the X-correlation measurement on the largest scales from 9 sigma to 5 sigma. The remaining X-correlation suggests the contamination in the quasar sample too great to allow a competitive constraint on fNL by correlations internal to this sample. The SDSS quasar catalog exhibits spurious number density fluctuations of ~2% rms, and we need a contamination level less than 1% (0.6%) in order to measure values of fNL less than 100 (10). Properly dealing with these systematics will be paramount for future large scale structure surveys that seek to constrain non-G.
1212.4526
Cross-correlation of SDSS DR7 quasars and DR10 BOSS galaxies: the weak luminosity dependence of quasar clustering at z~0.5
Shen, McBride, White, ... Padmanabhan, Ross, ... et al
Present the 2-pt X-correlation function of 8k quasars and 349 CMASS galaxies from BOSS at <z>~0.5 (0.3<z<0.9). The X-correlation function can be reasonably well fit bay a power-law model on projected scales of r_p=2-25 Mpc/h with r_0=6.61 Mpc/h and gamma=1.69 pm 0.07. Estimate a quasar linear bias of b_Q=1.38 at this redshift from the X-corr measurements. This linear bias corresponds to a characteristic host halo mass of 4e12 Msun/h, compared to 1e13 Msun/h characteristic host halo mass for CMASS galaxies. Divide the quasar sample in luminosity and constrain the luminosity dependence of quasar bias to be db_Q/dlogL=0.20 or 0.11 (depending on different luminosity divisions) for quasar luminosities -23.5>M_i>-25.5, impling a weak luminosity dependence of quasar clustering for the bright end of thequasar population at <z>~0.5. Compare meausrements with theoretical predictions, HOD models and mock catalogs. These comparisons suggest quasars reside in a broad range of host haloes, and the host halo mass distirbutions significantly overlap with each other for quasars at different luminosities, implying a poor correlation between halo mass and instantaneous quasar luminosity. Also find that the quasar HOD parameterization is largely degenerate such that different HODs can reproduce the CCF equally well, but with different outcomes such as the satellite fraction and host halo mass distribution. These results highlight the imitations and ambiguities in modeling the distribution of quasars with the standard HOD approach and the need for additional information in populating quasars in DM haloes with HOD.
1212.4661
Modern cosmology: interactive computer simulations that use recent observational surveys
Moldenhauer et al
Open-source computational tools for numerically modeling large-scale observational data sets using modern cosmology theory. Specifically, these tools will allow both students and researches to constrain the parameter values in competitive cosmological models, thereby discovering both the accelerated expansion of the universe and its composition (DM and DE). These programs have several features to help the non-cosmologist build and understanding of cosmological models and their relation to observational data: a build-in collection of several real observational data sets; sliders to vary the values of the parameters that define different cosmological models; real-time plotting of simulated data, and chi2 calculations of the goodness of fit for each choice of parameters (theory) and observational data (experiment). The current list of build-in observations includes several recent SNIa surveys, BAO, CMB, gamma-ray bursts, and measurements of the Hubble parameter. In this article, discuss specific results for testing cosmological models using these observational data. These programs can be found at its webpage.
1212.4726
Theoretical models of dark energy
Yoo, Watamabe
Solving fine-tuning and coincidence: quintessence, k-essence, coupled DE, and unified DE. Compare these models by presenting attractive aspects, new rising problems and possible solutions. Furthermore review modified gravity models that lead to late-time accelerated expansion without invoking a new form of DE; they contain f(R) gravity and the DGP model. Discuss observational constraints on those models and on future modified gravity theories. Review the inhomogeneous LTB model that drops and assumption of the spatial homogeneity of the Universe. Also present basics of cosmology and scalar field theory, which are useful eSpecially for students and novices to understand DE models.
1212.4759
An improved model for the infrared emission from the zodiacal dust cloud: cometary, asteroidal and interstallar dust
Rowan-Robinson, May
Model the IR emission from zodiacal dust from IRAS and COBE, with the aim of estimating the relative contributions of asteroidal, cometary and interstellar dust to the zodiacal cloud. Most important result is the detection of an isotropic component of FG radiation due to interstellar dust. The dust in the inner solar system is known to have a fan-dlike distribution. If this is assumed to extend to the orbit of Mars, find that cometary, asteroidal and interstellar dust account for 70%, 22% and 7.5% of the dust in the fan. Find a worse fit if the fan is assumed to extend to the orbit of Jupiter. Model is broadly consistent with the analysis by Divine (1993) of interplanetary dust detected by Ulysses and other spacecraft. Estimate of the mass-density of interstellar dust in the inner solar system is consistent with estimate fro Ulysses at 1.5 au, but is an order of magnitude higher than Ulysses estimates at r>4au. Only 1% of the zodiacal dust arriving at the earth would be interstellar in this model. Models can be further tested by ground-based kinematical studies of the zodiacal cloud, which need to extend over a period of years to monitor solar cycle variations in interstellar dust, by dynamical simulations, and by in situ measurements from spacecraft.
1212.4832
Multifractal analysis and lacunarity spectrum of the galaxies of the ninth Sloan digital sky survey (SDSS) data release
Chacon-Cardona, Casas-Miranda
Sample of 164k galaxies, use sliding-window technique to determine the multifractal dimension spectrum and its dependence on radial distance. Generalization of the concept of fractal dimension is used to analyze large-scale clustering of matter in complex systems. Likewise, the lacunarity spectrum, which is a quantity that complements the characterization of a fractal set by quantifying how the set fills the space in which it is embedded, is determined. Using these statistical tools, find that the clustering of galaxies exhibits fractal behavior that depends on the radial distance for all calculated quantities. A transition to homogeneity is not observed in the calculation of the fractal dimension of galaxies; instead, the galaxies exhibit a multifractal behavior whose dimensional spectrum does not exceed the physical spatial dimension for radial distances up to 180 Mpc/h from each center within the sample. Results and their implications are discussed in the context of the formation of large-scale structures in the Universe.
1212.4500
Systematic effects in large-scale angular power spectra of photometric quasars and implications for constraining primordial nongaussianity
Pullen, Hirata
Primordial non-Gaussianity of local type is predicted to lead to enhanced halo clustering on very large scales. Quasars at z>2 are promising tracers for constraining non-G using this effect. However, large-scale systematics can also mimic this signature of non-G. In order to assess the contribution of systematic effects, cross-correlate overdensity maps of photometric quasars from SDSS DR6 in different z ranges. Find that the maps are significantly correlated on large scales, even though the expectation is such that the angular distribution of quasars at different redshift to be uncorrelated. THis implies that the quasar maps are contaminated with systematic errors. Investigate the use of external templates that provide information on the spatial dependence of potential systematic errors to reduce the level of spurious clustering in the quasar data. Find that templates associated with stellar density, the stellar color locus, airmass, and seeing are major contaminants of quasar maps, with seeing having the largest effect. Using template projection, decrease the significance of the X-correlation measurement on the largest scales from 9 sigma to 5 sigma. The remaining X-correlation suggests the contamination in the quasar sample too great to allow a competitive constraint on fNL by correlations internal to this sample. The SDSS quasar catalog exhibits spurious number density fluctuations of ~2% rms, and we need a contamination level less than 1% (0.6%) in order to measure values of fNL less than 100 (10). Properly dealing with these systematics will be paramount for future large scale structure surveys that seek to constrain non-G.
1212.4526
Cross-correlation of SDSS DR7 quasars and DR10 BOSS galaxies: the weak luminosity dependence of quasar clustering at z~0.5
Shen, McBride, White, ... Padmanabhan, Ross, ... et al
Present the 2-pt X-correlation function of 8k quasars and 349 CMASS galaxies from BOSS at <z>~0.5 (0.3<z<0.9). The X-correlation function can be reasonably well fit bay a power-law model on projected scales of r_p=2-25 Mpc/h with r_0=6.61 Mpc/h and gamma=1.69 pm 0.07. Estimate a quasar linear bias of b_Q=1.38 at this redshift from the X-corr measurements. This linear bias corresponds to a characteristic host halo mass of 4e12 Msun/h, compared to 1e13 Msun/h characteristic host halo mass for CMASS galaxies. Divide the quasar sample in luminosity and constrain the luminosity dependence of quasar bias to be db_Q/dlogL=0.20 or 0.11 (depending on different luminosity divisions) for quasar luminosities -23.5>M_i>-25.5, impling a weak luminosity dependence of quasar clustering for the bright end of thequasar population at <z>~0.5. Compare meausrements with theoretical predictions, HOD models and mock catalogs. These comparisons suggest quasars reside in a broad range of host haloes, and the host halo mass distirbutions significantly overlap with each other for quasars at different luminosities, implying a poor correlation between halo mass and instantaneous quasar luminosity. Also find that the quasar HOD parameterization is largely degenerate such that different HODs can reproduce the CCF equally well, but with different outcomes such as the satellite fraction and host halo mass distribution. These results highlight the imitations and ambiguities in modeling the distribution of quasars with the standard HOD approach and the need for additional information in populating quasars in DM haloes with HOD.
1212.4661
Modern cosmology: interactive computer simulations that use recent observational surveys
Moldenhauer et al
Open-source computational tools for numerically modeling large-scale observational data sets using modern cosmology theory. Specifically, these tools will allow both students and researches to constrain the parameter values in competitive cosmological models, thereby discovering both the accelerated expansion of the universe and its composition (DM and DE). These programs have several features to help the non-cosmologist build and understanding of cosmological models and their relation to observational data: a build-in collection of several real observational data sets; sliders to vary the values of the parameters that define different cosmological models; real-time plotting of simulated data, and chi2 calculations of the goodness of fit for each choice of parameters (theory) and observational data (experiment). The current list of build-in observations includes several recent SNIa surveys, BAO, CMB, gamma-ray bursts, and measurements of the Hubble parameter. In this article, discuss specific results for testing cosmological models using these observational data. These programs can be found at its webpage.
1212.4726
Theoretical models of dark energy
Yoo, Watamabe
Solving fine-tuning and coincidence: quintessence, k-essence, coupled DE, and unified DE. Compare these models by presenting attractive aspects, new rising problems and possible solutions. Furthermore review modified gravity models that lead to late-time accelerated expansion without invoking a new form of DE; they contain f(R) gravity and the DGP model. Discuss observational constraints on those models and on future modified gravity theories. Review the inhomogeneous LTB model that drops and assumption of the spatial homogeneity of the Universe. Also present basics of cosmology and scalar field theory, which are useful eSpecially for students and novices to understand DE models.
1212.4759
An improved model for the infrared emission from the zodiacal dust cloud: cometary, asteroidal and interstallar dust
Rowan-Robinson, May
Model the IR emission from zodiacal dust from IRAS and COBE, with the aim of estimating the relative contributions of asteroidal, cometary and interstellar dust to the zodiacal cloud. Most important result is the detection of an isotropic component of FG radiation due to interstellar dust. The dust in the inner solar system is known to have a fan-dlike distribution. If this is assumed to extend to the orbit of Mars, find that cometary, asteroidal and interstellar dust account for 70%, 22% and 7.5% of the dust in the fan. Find a worse fit if the fan is assumed to extend to the orbit of Jupiter. Model is broadly consistent with the analysis by Divine (1993) of interplanetary dust detected by Ulysses and other spacecraft. Estimate of the mass-density of interstellar dust in the inner solar system is consistent with estimate fro Ulysses at 1.5 au, but is an order of magnitude higher than Ulysses estimates at r>4au. Only 1% of the zodiacal dust arriving at the earth would be interstellar in this model. Models can be further tested by ground-based kinematical studies of the zodiacal cloud, which need to extend over a period of years to monitor solar cycle variations in interstellar dust, by dynamical simulations, and by in situ measurements from spacecraft.
1212.4832
Multifractal analysis and lacunarity spectrum of the galaxies of the ninth Sloan digital sky survey (SDSS) data release
Chacon-Cardona, Casas-Miranda
Sample of 164k galaxies, use sliding-window technique to determine the multifractal dimension spectrum and its dependence on radial distance. Generalization of the concept of fractal dimension is used to analyze large-scale clustering of matter in complex systems. Likewise, the lacunarity spectrum, which is a quantity that complements the characterization of a fractal set by quantifying how the set fills the space in which it is embedded, is determined. Using these statistical tools, find that the clustering of galaxies exhibits fractal behavior that depends on the radial distance for all calculated quantities. A transition to homogeneity is not observed in the calculation of the fractal dimension of galaxies; instead, the galaxies exhibit a multifractal behavior whose dimensional spectrum does not exceed the physical spatial dimension for radial distances up to 180 Mpc/h from each center within the sample. Results and their implications are discussed in the context of the formation of large-scale structures in the Universe.
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